Motor-Mounted Internal Gear Pump and Electronic Equipment

ABSTRACT

A motor-mounted internal gear pump  80  includes: a pump part  81  which sucks and discharges hydraulic fluid; and a motor part  82  which drives the pump  81 . The pump part  81  includes: an inner rotor  1  with teeth on its outer surface; an outer rotor  2  with teeth on its inner surface to mesh with the teeth of the inner rotor; and pump casings  3, 4  which house the inner rotor  1  and the outer rotor  2 . The motor part  82  includes a rotator  11  and a stator  12  which rotates the rotator  11 . A common member  112  of permanent magnet material as resin containing magnetic powder serves as the rotator  11  and the outer rotor  2 . This structure assures further inexpensiveness and reliability while maintaining compactness and inexpensiveness in functions.

TECHNICAL FIELD

The present invention relates to a motor-mounted internal gear pump andelectronic equipment.

BACKGROUND ART

Internal gear pumps have long been known as pumps which discharge suckedliquid against pressure, and particularly have been popular as hydraulicsource pumps or oil feed pumps.

An internal gear pump includes, as main active components, a spur geartype inner rotor with teeth on its outer surface, and an annular outerrotor with teeth on its inner surface which has almost the same width asthe inner rotor. A pump casing, which has flat inner surfaces facingboth side faces of these rotors with a small gap, is provided to housethe rotors. The number of teeth of the inner rotor is usually onesmaller than that of the outer rotor, and the rotors rotate with theirteeth meshed with each other, like power transmission gears. As thegroove area changes with this rotation, the liquid trapped in thegrooves is sucked or discharged so that the function as a pump isperformed. When one of the inner and outer rotors is driven, the otherrotor, meshed with it, rotates as well. Since the center of rotation isdifferent between the rotors, each rotor must be pivotally supported ina rotatable manner individually. The pump casing has openings to flowchannels communicated with the outside, called a suction port and adischarge port. The suction port is designed to communicate with agroove whose volume increases and the discharge port is designed tocommunicate with a groove whose volume decreases. As for rotor profiles,typically, the outer rotor profile includes an arc and the inner rotorteeth are trochoidal teeth.

Since the internal gear pump rotates with its inner rotor and outerrotor meshed, when one rotor is driven, the other rotor rotates as well.When a motor part is integral with the outer surface of a pump part andthe rotator of the motor part is integral with the outer rotor and themotor part drives the outer rotor, this structure can be shorter than astructure in which the pump part and the motor part are arranged inseries along the axial direction and is thus suitable for a compactpump.

One example of this type of internal gear pump is the internal gear pumpas disclosed in Japanese Patent Application Laid-Open Publication No.H2-277983 (Patent Document 1). According to Patent Document 1, theinternal gear pump includes an internal gear which combines an outergear (outer rotor) having a rotor on its outer surface to face andcontact a stator fitted in a motor casing, with a given gap inside thestator in the radial direction, and an inner gear (equivalent to aninner rotor) to mesh with this outer gear, wherein both end faces of theinternal gear are liquid-tightly closed by end plates and one of the endplates has a suction port and a discharge port which communicate withthe internal gear. The end plates (pump casings) include a front casingand a rear casing; disc thrust bearings are disposed between the casingsand both sides of the internal gear pump; and both sides of the outergear are supported by the thrust bearings; both ends of a support shaftare fixed to the casings and the inner gear is rotatably supported bythe support shaft through a radial bearing; and also a liquid feedchannel is provided to allow some of the pressurized liquid on thedischarge side to flow between the rotor and stator and lubricate thebearings and flow back to the suction side.

Patent Publication 1: Japanese Patent Application Laid-Open PublicationNo. H2-277983

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, the internal gear pump described in Patent Document 1 has aproblem that since the outer gear and rotor are separate members,inevitably the size is considerable and the cost is high.

Furthermore, Patent Document 1 neither discloses the materials of therotor, outer gear, inner gear and end plates which constitute theinternal gear pump nor discloses that it is used in electronicequipment. If this internal gear pump is used in electronic equipment,such as a personal computer or server, it should meet the followingrequirements: mass productivity, long service life, the ability tomaintain high accuracy, less friction in sliding parts, low cost andlightness. Also, it has been found that since in consideration of thestorage temperature of the electronic equipment, an antifreeze liquidsuch as ethylene glycol is used as hydraulic fluid which flows in thepump for use in electronic equipment, compatibility between the internalgear and the antifreeze liquid must be taken into account.

An object of the present invention is to provide a motor-mountedinternal gear pump and electronic equipment which assure compactness,inexpensiveness and high reliability taking advantage of thefunctionality as an internal gear pump suitable for high liftapplication.

Means for Solving the Problems

In order to achieve the above object, in a first mode of the invention,a motor-mounted internal gear pump includes a pump part which sucks anddischarges hydraulic fluid, and a motor part which drives the pump part;the pump part includes an inner rotor with teeth on its outer surface,an outer rotor with teeth on its inner surface to mesh with the teeth ofthe inner rotor, and a pump casing which houses the inner rotor and theouter rotor, and the motor part includes a rotator, and a stator whichrotates the rotator, wherein a common member of permanent magnetmaterial as resin containing magnetic powder serves as the rotator andthe outer rotor.

Preferred concrete examples in the first mode of the present inventionare as follows.

(1) Water or a liquid containing water as an ingredient is used ashydraulic fluid which is sucked and discharged by the pump part and thecommon member for the rotator and the outer rotor is made of ferritebond magnet containing ferrite magnetic powder.(2) The common member for the rotator and the outer rotor is formed as amember whose magnetic force is strong on its outer surface side and weakon its inner surface side, and the stator is located around and outsidethe common member.(3) In the example mentioned above in (1), an antifreeze liquidcontaining water and an organic substance is used as the hydraulicfluid.(4) In the example mentioned above in (1), the common member is made ofPPS/ferrite bond magnet as PPS resin containing ferrite magnetic powder.(5) In the example mentioned above in (1), the pump casing consists oftwo casings, a first casing and a second casing, which are connected;shoulder sections protruding inward are formed on the first casing andthe second casing respectively in a way to face each other; and annularbracket sections axially extending from the inner teeth are formed atboth sides of the outer peripheral part of the common member; theannular bracket sections are fitted to the outer surfaces of therespective shoulder sections of the first casing and the second casing;and the stator is located around and outside the common member.(6) In the example mentioned above in (1), the pump casing is made ofPPS carbon fiber resin as PPS resin containing carbon fiber or PPS glassfiber resin as PPS resin containing glass fiber.(7) In the example mentioned above in (1), the inner rotor is made ofPPS carbon fiber resin as PPS resin containing carbon fiber, or POMresin.(8) In the example mentioned above in (5), the first casing and thesecond casing are made of PPS carbon fiber resin as PPS resin containingcarbon fiber.(9) In the example mentioned above in (8), an outer peripheral part ofeither of the first casing and the second casing is extended axially toform a can for sealing between the rotator and the stator, and thestator is fitted outside the can.

In a second mode of the present invention, a motor-mounted internal gearpump includes: a pump part which sucks and discharges hydraulic fluid,and a motor part which drives the pump part; the pump part includes aninner rotor with teeth on its outer surface, an outer rotor with teethon its inner surface to mesh with the teeth of the inner rotor, and apump casing which houses the inner rotor and the outer rotor, and themotor part includes a rotator, and a stator which rotates the rotator,wherein the rotator is made of PPS resin/ferrite bond magnet as PPSresin containing ferrite magnetic powder.

A preferred concrete example in the second mode of the present inventionis as follows.

(1) The pump casing is made of PPS carbon fiber resin as PPS resincontaining carbon fiber and the inner rotor is made of PPS carbon fiberresin as PPS resin containing carbon fiber.

A third mode of the present invention is electronic equipment in whichone of the above motor-mounted internal gear pumps is mounted as aliquid circulation source and an antifreeze liquid composed of water andan organic substance is used as hydraulic fluid.

EFFECT OF THE INVENTION

According to the present invention, it is possible to provide amotor-mounted internal gear pump and electronic equipment which assurecompactness, inexpensiveness and high reliability taking advantage ofthe functionality as an internal gear pump suitable for high liftapplication.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a motor-mounted internal gear pump, a manufacturing method thereofand electronic equipment according to an embodiment of the presentinvention will be described referring to FIGS. 1 to 6.

First, the general structure of a motor-mounted internal gear pumpaccording to this embodiment will be described referring to FIGS. 1 and4. FIG. 1 is a longitudinal sectional view of a motor-mounted internalgear pump 80 according to an embodiment of the present invention; FIG. 2is a sectional front view showing the left half of the pump 80 in FIG.1; FIG. 3 is an exploded perspective view of the pump part of the pump80 in FIG. 1; and FIG. 4 is a sectional view showing how to connect thecasings of the pump 80 in FIG. 1.

The pump 80 is a motor-mounted internal gear pump which includes a pumppart 81 which sucks hydraulic fluid and discharges it, a motor part 82which drives the pump part 81, and a control part 83 which controls themotor part 82.

The pump part 81 includes an inner rotor 1 made of resin, an outer rotor2 made of resin, a front casing (first casing) 3 made of resin, a rearcasing (second casing) 4 made of resin and an internal shaft 5 made ofmetal. The front casing 3 and rear casing 4 are members which constitutea pump casing: in other words, the pump casing member consists of twoseparate pump casing members. The rear casing 4 includes a can 6, aflange 18 and a cover 13. The internal shaft 5, which constitutes ashaft for supporting the inner rotor, is a member separate from thefront casing 3 or the rear casing 4 in this embodiment.

The motor part 82 includes a rotator 11 as a permanent magnet, a stator12, and a can 6. The can 6 is shared by the pump part 81 and the motorpart 82.

The inner rotor 1 of the pump part 81 is similar in shape to a spur gearand has trochoidal teeth 1 a on its outer surface. Strictly speaking thetooth surface is slightly angled in the axial direction, making an anglecalled a “draft angle” which facilitates drafting in injection molding.Also, the inner rotor 1 has, in its center, an axial hole 1 b with asmooth inner surface which penetrates it axially. Both end faces 1 c ofthe inner rotor 1 are flat and smooth and constitute sliding surfacesbetween the flat inner faces 25, 26 as the end faces of shouldersections 22 protruding inward from the front casing 3 and rear casing 4.

The inner rotor 1 is made of a self-lubricating synthetic resin in whichswelling or corrosion caused by water or an aqueous solution isnegligible. Concretely, it is made of PPS carbon fiber resin as PPS(polyphenylene sulfide) resin containing carbide fiber. Because of this,the inner rotor 1 has sufficient strength and wear resistance and can bean inexpensive inner rotor 1. Instead of PPS carbon fiber resin, POM(polyacetal) resin may be used. Since POM is low in friction resistanceand low in sliding resistance, it improves the pump efficiency. Alsosince it is a soft material, it can alleviate impact load, therebysuppressing vibration noise caused by rotor motion. Although thesematerials have a water-absorbing property and transmit water, there isno problem since they are used for the inner rotor 1. When it absorbshot water, it may deform; however, if it is profiled to compensate forsuch deformation, deformation is mitigated. At low temperatures, the gapbetween both rotors 1, 2 increases but if an antifreeze liquid composedof water and an organic substance is used for the hydraulic fluid, theviscosity of the antifreeze liquid increases and the pump efficiencyimproves, thereby preventing performance deterioration.

The outer rotor 2 takes the form of an annular internal gear havingalmost the same tooth width as the inner rotor 1 and has arched teethwhere the number of teeth is one larger than the number of teeth of theinner rotor 1. The teeth 2 a of the outer rotor 2 as a spur gear have asectional profile which is almost constant in the axial direction;however, they may be slightly angled in the axial direction, or have anangle called a “draft angle” to facilitate drafting in injectionmolding. In this case, the inner rotor 1 should have a similar draftangle and the inner rotor 1 and the outer rotor 2 are angled in oppositedirections and the rotors 1, 2 are meshed so that the inner teethdiameter of the outer rotor 2 increases in the direction in which theouter teeth diameter of the inner rotor 1 increases. This can preventthe meshing surfaces of the rotors 1, 2 from contacting each otherunevenly in the axial direction. Both end faces 2 b of the teeth of theouter rotor 2 are flat and smooth and constitute sliding surfacesbetween the flat inner faces 25, 26 of the front casing 3 and rearcasing 4 and function as thrust bearings.

The outer rotor 2 has almost the same width as the inner rotor 1 exceptits outer periphery, and the outer rotor 2 is disposed outside the innerrotor 1 in a way that both end faces of the inner rotor 1 almostcoincide with those of the outer rotor 2. Annular bracket sections 21,which protrude axially from the teeth portion (which has almost the sametooth width as the inner rotor 1 located inside), are formed on theouter periphery of the outer rotor 2. The inner surfaces of the bracketsections 21 are smooth and constitute sliding surfaces between the outersurfaces 27, 28 of the shoulder sections 22.

The outer rotor 2 and inner rotor 1 are designed to rotate between thefront casing 3 and rear casing 4 while meshed with each other. A bearingof the internal shaft 5 with a smooth outer surface is fitted into thecentral axial hole of the inner rotor 1 with a small gap, and thus theinner rotor 1 is pivotally supported by the internal shaft 5 in arotatable manner. The internal shaft 5 does not rotate because it istightly fitted into the front casing 3 and rear casing 4.

A permanent magnet as the rotator 11 of the motor part 82 is integratedwith the outside of the outer rotor 2. In this embodiment, resin mixedwith magnetic powder is used to form the rotator 11 integral with theouter rotor 2. In other words, the rotator 11 of the motor part 82 andthe outer rotor 2 of the pump part 81 constitute a common member 112made of permanent magnet containing magnetic powder. This means that therotator 11 and the outer rotor 2 can be compact and manufactured at lowcost. The rotator 11 provides alternate polarities in the radialdirection and when viewed from outside, it has N and S poles arrangedalternately along its circumference.

In this embodiment, the common member 112 is made of ferrite bond magnetcontaining ferrite magnet powder. Therefore, even if water or a liquidcontaining water as an ingredient is used as hydraulic fluid, the magnetneither corrodes nor rusts and can be manufactured at low cost. Thiscommon member 112 is also made of PPS/ferrite bond magnet as PPS resincontaining ferrite magnetic powder. Therefore, the magnetic property asthe rotator 11 of the motor part 82 is improved, high precision teethfor the pump part 81 can be formed, and a low-friction, low-wear slidingproperty is achieved in the portion which functions as a bearing, andalso formability is high and stability against corrosion in water ishigh.

In this embodiment, the common member 112 is formed cylindrically sothat the magnetic force of its outer surface is strong and that of itsinner surface is weak, and since the stator 12 is located outside theouter surface of the common member 112, magnetization from the outersurface is easy and even if ferrite bond magnet, usually inexpensive andweaker in magnetic force than neodymium magnet, is used, the function asthe rotator 11 can be well performed.

Furthermore, in this embodiment, shoulder sections 22, protrudinginward, are respectively formed on the front casing 3 and rear casing 4in a way to face each other; and annular bracket sections 21, protrudingaxially from the teeth portion of the inner surface, are formed at bothsides of the outer periphery of the common member 112 and the annularbracket sections 21 are fitted to the outer surfaces 27, 28 of therespective shoulder sections 22 of the front casing 3 and rear casing 4,so that the portion which functions as the rotator 11 can be increasedin size axially, which helps the use of ferrite bond magnet which isinexpensive and weak in magnetic force.

It is possible that a composite structure serves as both the outer rotor2 and the rotator 11 where the outer surface including the outer rotor2's bracket sections is of PPS/ferrite bond magnet and the teeth portionis of PPS carbon fiber. In that case, if PPS/ferrite bond magnet, fromwhich it is difficult to make a complicated shape, is used to make asimple cylindrical shape and PPS resin is used to make the teeth portionwhich requires accuracy, teeth with low loss and low wear are formedwithout hard ferrite powder in the surface of meshing with the innerrotor 1.

The internal shaft 5 includes: a cylindrical bearing 51 which has anoutside diameter slightly smaller than the inside diameter of the axialhole 1 b of the inner rotor 1 and is slightly longer than the toothwidth of the inner rotor 1 in the axial direction; and a fitting part 53which extends from both end faces of the bearing 51 in both axialdirections and has an outside diameter smaller than the outside diameterof the bearing 51. Concretely, the axial length of the bearing 51,located in the center of the internal shaft 5, is slightly (for example,0.05-0.1 mm) longer than the tooth width of both rotors. The cylindricalfitting part 53, located at each end of the bearing 51, is concentricwith the bearing 51. The bearing 51 and the fitting part 53 are parts ofthe internal shaft 5 which are all made of the same metal material, andintegral with each other. The internal shaft 5, made of a metalmaterial, is superior in strength and dimensional accuracy to the innerrotor 1, outer rotor 2, front casing 3 and rear casing 4 which are madeof synthetic resin.

The internal shaft 5 also has the function as a structural member whichconnects the front casing 3 and the rear casing 4. Its fitting part 53is inserted and fixed into fitting holes 27 a, 28 a made in the flatinner surfaces 25, 26 of both casings 3, 4. In this condition, the stepfaces (both end faces of the bearing 51) 51 a as boundaries between thebearing 51 and the fitting part 53 are in close contact with the flatinner surfaces 25, 26 of the casings. This means that the length of thebearing 51 is equal to the distance (interval) between both flat innersurfaces 25, 26, and both rotors 1, 2 are inside the flat inner surfaces25, 26 as the axial end faces of the front casing 3 and rear casing 4,with a small gap. The fitting holes of the front casing 3 and rearcasing 4 are eccentric with respect to the outer surfaces 27, 28 of theshoulder sections 22 in a way to accommodate both rotors 1, 2 which aremeshed.

The shoulder sections 22 of the front casing 3 and rear casing 4protrude inward in a way to face each other. The outer surfaces 27, 28of the shoulder sections 22 are fitted to the inner surfaces of thebracket sections 21 of the outer rotor 2 with a small gap; and theshoulder sections 22 of the front casing 3 and rear casing 4 pivotallysupport both sides of the outer rotor 2 in a rotatable manner,functioning as radial bearings. The shoulder sections 22 of the frontcasing 3 and rear casing 4 are in a positional relation as if theyoriginated from a single cylinder.

The front casing 3, one of the two pump casing members, has a holecalled a suction port 8 and a hole called a discharge port 10 in itsflat inner surface 25. The suction port 8 and the discharge port 10 areholes whose profile extends inside the tooth-base circle of the innerrotor 1 and outside the tooth-base circle of the outer rotor 2 (sincethe outer rotor 2 is an internal gear, its tooth-base circle diameter islarger than its tooth-tip circle diameter). The suction port 8 faces aworking chamber 23 whose volume increases and the discharge port 10faces a working chamber 23 whose volume decreases. When the volume of aworking chamber 23 is maximized, either port 8, 9 does not face theworking chamber 23 or is communicated with it only through a smallsectional area.

The suction port 8 and discharge port 10 are respectively communicatedfrom the innermost port grooves through an L-shaped flow channel with asuction hole 7 and a discharge hole 9 which are open to the outside.Midway in the flow channel from the discharge port 10 to the dischargehole 9, there is a branched communication path 9 a which communicateswith an internal space 24 facing the outer surface of the outer rotor 2.The internal space 24 is a space surrounded by the front casing 3 andthe rear casing 4 including the can 6.

The can 6, a thin-walled cylinder, is located with a small gap from theouter surface of the rotator 11 (for example, gap of 1 mm or less), sothat the rotator 11 can rotate together with the outer rotor 2.

The rear casing 4, one of the two casing members, has a cylindrical can6 covering the outside of the outer rotor 2 and axially extendingoutward from the portion constituting its flat inner surface 26, wherethe can 6 side is softer than the flat inner surface 26 side in terms ofaxial rigidity; and at the tip side of the can 6, it is connected withthe front casing 3, one of the two casing members. In other words, thecan 6 is part of the rear casing 4 and refers to a cylindrical thinportion extending frontward and outward from the portions constitutingthe flat inner surface and shoulder section.

The front casing 3 and rear casing 4 contact each other on a cylindricalsurface called a fitting surface 16, engaging with each other withfreedom in axial movement while binding each other in the radialdirection. The fitting surface 16 consists of a fitting surface betweenthe inner surface of the tip of the can 6 and the outer surface of theouter annular part 29 formed inside the front casing 3. A dent is formedin the inner surface of the tip of the can 6 adjacent to the fittingsurface 16 and an O ring 14 inserted into this dent keepsconfidentiality between the front casing 3 and rear casing 4. Suchstructure allows the front casing 3 and rear casing 4 to be combined ina confidentiality manner while assuring freedom in the axial direction.

The front casing 3 and rear casing 4 are made of PPS carbon fiber resin,PPS resin containing carbon fiber. The front casing 3 and rear casing 4of PPS carbon fiber resin are less water-absorbent and less deform dueto water absorption and less deform thermally and arecorrosion-resistant against an antifreeze liquid and heat-resistant.Since PPS carbon fiber resin is an insulating material, it is effectivein prevention of ground leakage and also it transmits less water andwell slides on bearings so that wear rarely occurs and long life andhigh reliability are expected and forming can be done with highprecision.

Plural welding projections 41 which are annular and oriented rearwardare formed near the outer surface of the front casing 3 and annularwelding grooves 42 into which the welding projections 41 are insertedare formed in the flange 18 of the rear casing 4. In this embodiment, asshown in FIG. 4, the tip of a welding projection 41 has a slantedsurface and the bottom of a welding groove 42 has a slanted surface tomatch the abovementioned slanted surface and welding tools 43, 44 arepushed against the outer surface of the front casing 3 and the flange 18of the rear casing 4 from both sides and micro-vibrations are given tothe welding tools 43, 44 with a force applied to the welding tools 43,44. Concretely, the welding tools 43, 44 are attached to an ultrasonicwelder to give them ultrasonic vibrations. Consequently, the surface ofcontact between both casings 3, 4 generates heat due to micro-vibrationfriction and melts and they fuse with each other; after vibrations stop,as the temperature goes down, they are re-solidified and connected. Forthis reason, the back side of the welding projection 41 of the frontcasing 3 and the back side of the welding groove 42 of the rear casing 4should be flat and open so that the welding tools 43, 44 can be placedin tight contact with them.

The groove on the rear casing 4 into which the welding tool 44 isinserted is an annular groove into which the stator 12 is inserted afterwelding and can be smaller and simpler in shape than a groove dedicatedto welding.

Any contact that limits axial movement, except two points of contact,contact between the welding projection 41 and the welding groove 42 andcontact between the internal shaft 5 step and the flat inner surface 25,26, should be eliminated before completion of welding. The can 6 isthin-walled and the can and its vicinity are softer than the flat innersurfaces, the shoulder sections and the areas around welding points.This establishes a positional relationship among members in thefollowing order.

First, the fitting part 53 of the internal shaft 5 is inserted in therear casing 4; the inner rotor 1 and outer rotor 2 are fitted into theinternal shaft 5; and the front casing 3 with the O ring 14 fittedthereon is fitted to the rear casing 4. In this condition, the weldingtools 43, 44 are applied to both casings 4, 5 from both sides andultrasonic vibrations are given to them while they are pushed with aprescribed force. Consequently the point of contact between the weldingprojection 41 and welding groove 42 melts and the front casing 3 andrear casing 4 come closer to each other. In this process, the step faces51 a of the internal shaft 5 come into tight contact with the flat innersurfaces 25, 26. As welding goes on, the can 6 of the rear casing 4 andits vicinity are elastically deformed and welding goes deeper.Vibrations are stopped with a force on the welding tools 43, 44 and themolten welded parts cool down and solidify, settling into shape. Evenafter the welding tools are removed, the step faces 51 a of the internalshaft 5 remain in contact with the flat inner surfaces 25, 26 and thatcontact force remains a reactive force against elastic deformation ofthe can 6 and its vicinity.

The internal shaft 5 is made of metal and easier to manufacture withrequired dimensional accuracy in the axial direction than the resincasing members 3, 4. It is also advantageous in that dimensionalaccuracy in the tooth width direction is assured in its central partadjacent to the teeth of the rotors 1, 2. It is far easier to maintainaccuracy than in the method in which accuracy in the distance betweenboth flat inner surfaces 25, 26 is assured only by dimensional accuracyof the casings 3, 4 through the outer periphery of the can 6, etc.without relying on accuracy of the internal shaft 5. Hence the structurein this embodiment is effective in keeping the gap at tooth end faces,which has a large influence on pump performance and reliability,adequate

The welding projection 41 is annular but not a continuous circle andthere are missing parts in the circumference as shown in FIG. 2. Thereason for this is that a pushing force as applied to a limited area ismore concentrated than as applied to the whole circumference and thuswelding is done more securely. The suction and discharge flow channelslie in the missing parts in order to prevent interference between thewelding tool 43 and these flow channels.

Thanks to the function of the fitting surface 16, the two casings arecombined with high positioning accuracy in the radial direction, andtheir axial positional accuracy is maintained by contact between theinternal shaft 5 and the flat inner surfaces 25, 26. The internal space24 is hermetically sealed by the O ring 14 and there are no holes orfitting surfaces communicated with the outside except the suction hole 8and discharge hole 10 and this simple structure is highly liquid-tight.Hence, it prevents liquid leakage with reliability.

The cover 13 is integrally molded as a backwardly folded extension fromthe flange 18 on the front side of the can 6 which is continuous withthe rear casing 4. The cover 13, which covers the outer surface of thestator 12 of the motor part 82, is useful in preventing electric shock,keeping a good appearance and shutting off the noise.

The stator 12 is press-fitted into the outer surface of the can 6outside the can 6 and opposite to the rotator 11 where the stator 12consists of a winding around a comb-shaped iron core. The stator 12 isfitted into a circular groove formed between the can 6 and the cover 13.Since the motor part 82, composed of the rotator 11 and the stator 12,is located around the pump part 81, composed of the inner rotor 1 andthe outer rotor 2, namely the motor part 82 and the pump part 81 are notarranged in series along the axial direction, the pump 80 is thin andcompact.

The control part 83, which is intended to control the motor part 82, isequipped with an inverter electronic circuit for driving a brushless DCmotor. Since the motor part 82 is located around the pump part 81 asmentioned above, the control part 83 can be located on the rear sidewhere the suction hole 7 and the discharge hole 9 of the pump part 81are not located.

A power device 32 as a main electronic component is mounted on a circuitboard 31, constituting an inverter circuit for driving a brushless DCmotor. The circuit board 31 is fixed to the rear casing 4 by caulking,or passing a projection 45 on the back of the rear casing 3 through ahole in its center. The power device 32 contacts the rear casing 4through the circuit board 31. Consequently, heat generated in theinverter circuit can be passed through the rear casing 4 into thehydraulic fluid in the pump part 81. The circuit board 31 is connectedwith one end of the winding of the stator 12 and also with a power line33 for external power supply, a rotation output line 34 for transmittingrotation speed information by pulses and a common grounding line forthem.

The brushless DC motor includes: the motor part 82 having the rotator 11as permanent magnet, and the stator 12; and the control part 83 havingthe inverter electronic circuit. The structure that the rotator 11 isinside the thin-walled can 6 and the stator 12 is outside the can 6 iscalled a “canned motor”. Since the canned motor does not require a shaftseal, etc. and transmits the turning force to the inside of theso-called can 6 by the use of a magnetic force, it is suitable for thestructure of a positive displacement pump which pumps out the hydraulicfluid through change in the volume of the working chambers 23 whileisolating the fluid from the outside.

When the pump 80 has dimensional relations as shown in FIG. 5, theobject of the present invention is achieved better. When the width ofthe inner rotor 1 and the tooth width of the outer rotor 2 are expressedas 1, the outside diameter of the inner rotor should be 1.7-3.4, theinside diameter of the outer rotor bracket sections should be 2.5-5, andthe axial length of the outer rotor bracket sections should be 0.4-0.8.

If the outside diameter of the inner rotor 1 is above this range, therate of internal leakage (back flow from the higher pressure dischargeport communicating side to the suction port communicating side, whichdeteriorates pump performance) would increase, deteriorating pumpperformance. If it is below the range, the velocity of flow wouldincrease at opening areas where the working chambers communicate withthe suction or discharge port, leading to increased pressure loss anddeterioration in pump performance.

The inside diameter of the bracket section 21 of the outer rotor 2 mustbe geometrically larger than the outside diameter of the inner rotor 1.At the same time, if it is above this range, frictional force andinternal leakage from bearing surfaces would increase, leading todeterioration in pump performance.

If the axial length of the outer rotor bracket section 21 is below thisrange, the bearing surface pressure might increase and thus frictionalwear might increase, leading to shorter pump life and lower reliability.If it is above this range, it is disadvantageous because unevenness incontact easily occurs due to errors in bearing surface cylindricalityand concentricity, etc.

It is recommended that the inner rotor rotation speed be within therange of 2500-5000 rpm. If the rotation speed is slower than this, theratio of internal leakage to transportation flow rate would increase,leading to deterioration in pump efficiency. If it is faster than this,vibration noise generated by the pump would increase.

Next, how the pump 80 works will be explained referring to FIGS. 1 to 5.

By giving 12 V DC power to the power line 33 to supply electric currentto the motor drive circuit of the control part 83, electric current isfed through the power device 32 to the winding of the stator 12. Thisstarts the motor part 82 and controls it to rotate it at a presetrotation speed. Since the power device 32 outputs rotation informationon the rotator 11 as a pulse signal through the rotation output line 34,a higher-level control apparatus which receives the signal can confirmthe operating condition of the pump 80.

As the rotator 11 of the motor part 82 rotates, the outer rotor 2,united with it also rotates; as the rotation is transmitted like anordinary internal gear, the inner rotor 1, meshed with it, also rotates.The volume of working chambers 23 formed in the grooves of the tworotors 1, 2 increases or decreases as both rotors 1, 2 rotate. As shownin FIG. 2, when the teeth of the inner rotor 1 and outer rotor 2 aremeshed deepest, the volume of the working chamber 23 at the bottom isthe minimum and the volume of the working chamber 23 at the top is themaximum. Hence, when the rotors rotate counterclockwise in FIG. 2, theworking chambers 23 in the right half move up and their volumeincreases, while the working chambers 23 in the left half move down andtheir volume decreases. All the sliding parts pivotally supporting bothrotors 1, 2 are immersed in the hydraulic fluid and therefore theirfriction is small and abnormal wear is prevented.

The hydraulic fluid passes through the suction hole 7 and then thesuction port 8 and is sucked into the working chambers 23 whose volumeis increasing. As the rotors rotate, the working chamber 23 whose volumeis maximized leaves the profile of the suction port 8 and finishes itssuction process, then communicates with the discharge port 10. Then, thevolume of the working chamber 23 begins to decrease and the hydraulicfluid in the working chamber 23 is discharged through the discharge port10. The discharged hydraulic fluid is sent out through the dischargehole 9. Since the branched communication path 9 a lies midway in thedischarge flow channel, the inner pressure of the internal space 24 ismaintained at a discharge pressure level.

In this embodiment, since the suction flow channel is short, thenegative pressure for suction is small, which prevents cavitation. Inaddition, a relatively high discharge pressure is applied to the innersurface of the can 6 to push and expand it outward and therefore eventhough the can 6 is thin-walled, it cannot be so deformed inward as totouch the rotator 11. At the same time, leakage from the gap as a radialbearing formed on the bracket section 21 of the outer rotor 2 can bereduced. The reason is that although the outward force of leakage fromthis gap is increased by a centrifugal force, if the inner pressure ofthe internal space 24 around it is high, there is an action which pushesit back.

In the power device 32, which must be cooled because it generates heatduring operation, the heat passes through the wall of the rear casing 4which the device contacts through the circuit board 31, and moves to thehydraulic fluid flowing in the internal space 24 before being releasedoutside. Since the hydraulic fluid in the internal space 24 is alwaysstirred and successively replaced due to minor leaks from the radialbearing surface, it carries away the heat efficiently. Since the insideof the pump 80 is cooled efficiently as described above, a heat sink orcooling fan for cooling the power device 32 is not needed. Similarly,the heat generated by motor loss in the rotator 11 or the stator 12 iscarried away efficiently, which prevents an abnormal temperature rise.

Next, electronic equipment which has the above pump 80 will be describedreferring to FIG. 6. FIG. 6 is a perspective view showing a personalcomputer system configuration with a computer in its upright position.The electronic equipment shown in FIG. 4 is a desk top personal computersystem.

The personal computer system 60 includes a personal computer 61A, adisplay unit 61B, and a keyboard 61C. A liquid-cooling system 69 ishoused in the personal computer 61A together with a CPU (centralprocessing unit) 62 and consists of a closed loop system in which aliquid reservoir 63, a pump 80, a heat exchanger 65, a heat radiatingplate A66 and a heat radiating plate B67 are connected in the order ofmention by tubing. This liquid-cooling system 69 is primarily intendedto convey out the heat generated by the CPU 62 housed in the personalcomputer 61A and keep the temperature rise of the CPU 62 below aprescribed level. The liquid-cooling system 69, which uses, as a heattransfer medium, water or an aqueous liquid such as an antifreeze liquidcomposed of water and an organic substance (ethylene glycol, etc),features a higher heat transfer capability and lower noise than anair-cooling system, so it is suitable for cooling the CPU 62 whichgenerates much heat.

The liquid being conveyed (hydraulic fluid) and air are filled in theliquid reservoir 63. The liquid reservoir 63 and the pump 80 are placedside by side where the outlet of the liquid reservoir 63 and the suctionhole of the pump 80 are connected by tubing. The heat exchanger 65 isbonded to the heat radiating surface of the CPU 62 through thermallyconductive grease. The discharge hole of the pump 80 and the inlet ofthe heat exchanger 65 are communicated by tubing. The heat exchanger 65is communicated with the heat radiating plate A66 by tubing; and theheat radiating plate A66 is communicated with the heat radiating plateB67 by tubing; and the heat radiating plate B67 is communicated with theliquid reservoir 63 by tubing. The heat radiating plate A66 and the heatradiating plate B67 are so located as to allow heat radiation fromdifferent surfaces of the personal computer 61A.

The pump 80 is connected with the power line 33 from a 12 V DC powersupply usually provided in the personal computer system 60 and therotation output line 34 is connected with the electronic circuit of thepersonal computer system 60 as a higher-level control apparatus.

Next, how this liquid-cooling system 69 works will be explained. As thepersonal computer system 60 is started, power is supplied, the pump 80begins running and the liquid being conveyed begins circulating. Theliquid is sucked from the liquid reservoir 63 into the pump 80 andpressurized by the pump 80 and sent to the heat exchanger 65. The liquidsent from the pump 80 to the heat exchanger 65 absorbs the heat emittedfrom the CPU 62 and the liquid temperature rises. Then, the heat of theliquid is exchanged for outside air through the heat radiating plate A66and the heat radiating plate B67 (heat is released to the outside) andconsequently the liquid temperature falls, then the liquid returns tothe liquid reservoir 63. This process is repeated so that the CPU 62 iscontinuously cooled.

Since the pump 80 is an internal gear pump as a kind of positivedisplacement pump, even if it is started in a dry (no liquid) condition,it has the ability to make the suction hole have a negative pressure.Therefore, even when the liquid comes through a tube above the liquidlevel inside the liquid reservoir 63 or when the pump 80 is located at ahigher position than the liquid level, the pump 80 has a self-primingability to suck liquid without priming water. The internal gear pump 80has a higher pressurizing ability than a centrifugal pump, etc, so itcan also be used in such a condition that the liquid passes through theheat exchanger 65 and the heat radiating plates 66, 67 and thus liquidpressure loss increases. Particularly when the heat density of the CPU62 is high, in order to increase the heat exchange area, the flowchannel inside the heat exchanger 65 must be elongated by folding it;thus a liquid cooling system which uses a centrifugal pump, etc. wouldbe difficult to use because of increased pressure loss in the liquidpassing through the channel, while the liquid cooling system 69according to this embodiment can cope with such a situation.

In the liquid cooling system 69 according to this embodiment, the liquidbeing conveyed passes through the heat radiating plates 66, 67 justafter the outlet of the heat exchanger 65 where the liquid temperatureis highest, and the liquid temperature falls, so the temperature of theliquid reservoir 63 and pump 80 is maintained at a relatively low level.For this reason, the internal parts in the pump 80 provide higherreliability than in a high temperature environment.

As a result of operation of the liquid cooling system 69, thetemperature of each of the components through which the liquidcirculates is determined and the temperature is monitored by a thermosensor (not shown). If insufficiency of the cooling performance isconfirmed by detection of a temperature above a prescribed level, acommand is given to increase the rotation speed of the pump 80 toprevent an excessive temperature rise. Contrarily, if the coolingperformance is too high, the rotation speed is decreased. The rotationoutput signal from the pump 80 is always monitored; if no rotationsignal is sent and there is an abnormal change in the liquidtemperature, the pump 80 is considered to be out of order and thepersonal computer system 60 enters an emergency mode. In the emergencymode, a fatal hardware damage is prevented by taking minimum necessarysteps such as decreasing the CPU speed and saving current program data.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] is a longitudinal sectional view of a motor-mounted internalgear pump according to an embodiment of the present invention.

[FIG. 2] is a sectional front view showing the left half of the pump inFIG. 1.

[FIG. 3] is an exploded perspective view of the pump part of the pump inFIG. 1.

[FIG. 4] is a sectional view showing how to connect the casings of thepump in FIG. 1.

[FIG. 5] is a dimensional drawing of the inner rotor and outer rotor ofthe pump in FIG. 1.

[FIG. 6] is an explanatory view of electronic equipment with a coolingsystem having the pump in FIG. 1.

EXPLANATION OF REFERENCE NUMERALS

-   1 . . . Inner rotor-   1 a . . . Teeth-   1 b . . . Axial hole-   1 c . . . End face-   2 . . . Outer rotor-   2 a . . . Teeth-   2 b . . . End face-   3 . . . Front casing-   4 . . . Rear casing-   5 . . . Internal shaft-   6 . . . Can-   7 . . . Suction hole-   8 . . . Suction port-   9 . . . Discharge hole-   9 a . . . Communication path-   10 . . . Discharge port-   11 . . . Rotator-   12 . . . Stator-   13 . . . Cover-   14 . . . O ring-   16 . . . Fitting surface-   18 . . . Flange-   21 . . . Bracket section-   22 . . . Shoulder section-   23 . . . Working chamber-   24 . . . Internal space-   25 . . . Front casing flat inner surface-   26 . . . Rear casing flat inner surface-   27, 28 . . . Shoulder section outer surfaces-   27 a, 28 a . . . Fitting holes-   29 . . . Outer annular part-   31 . . . Circuit board-   32 . . . Power device-   33 . . . Power line-   34 . . . Rotation output line-   41 . . . Welding projection-   42 . . . Welding groove-   43 . . . Welding tool-   44 . . . Welding tool-   51 . . . Bearing-   51 a . . . Step face-   53 . . . Fitting part-   60 . . . Personal computer system-   61A . . . Personal computer-   61B . . . Display unit-   61C . . . Keyboard-   62 . . . CPU-   63 . . . Liquid reservoir-   65 . . . Heat exchanger-   66 . . . Heat radiating plate A-   67 . . . Heat radiating plate B-   69 . . . Liquid-cooling system (cooling system)-   80 . . . Motor-mounted internal gear pump-   81 . . . Pump part-   82 . . . Motor part-   83 . . . Control part-   112 . . . Common member

1. A motor-mounted internal gear pump, comprising: a pump part whichsucks and discharges hydraulic fluid; and a motor part which drives thepump part, the pump part including: an inner rotor with teeth on itsouter surface; an outer rotor with teeth on its inner surface to meshwith the teeth of the inner rotor; and a pump casing which houses theinner rotor and the outer rotor; and the motor part including: arotator; and a stator which rotates the rotator, wherein a common memberof permanent magnet material as resin containing magnetic powder servesas the rotator and the outer rotor.
 2. The motor-mounted internal gearpump according to claim 1, wherein: water or a liquid containing wateras an ingredient is used as hydraulic fluid which is sucked anddischarged by the pump part; and the common member for the rotator andthe outer rotor is made of ferrite bond magnet containing ferritemagnetic powder.
 3. The motor-mounted internal gear pump according toclaim 1, wherein: the common member for the rotator and the outer rotoris formed as a member whose magnetic force is strong on its outersurface side and weak on its inner surface side; and the stator islocated around and outside the common member.
 4. The motor-mountedinternal gear pump according to claim 2, wherein an antifreeze liquidcontaining water and an organic substance is used as the hydraulicfluid.
 5. The motor-mounted internal gear pump according to claim 2,wherein the common member is made of PPS/ferrite bond magnet as PPSresin containing ferrite magnetic powder.
 6. The motor-mounted internalgear pump according to claim 2, wherein: the pump casing consists of twocasings, a first casing and a second casing which are connected;shoulder sections protruding inward are formed on the first casing andthe second casing respectively in a way to face each other; annularbracket sections axially extending from the inner teeth are formed atboth sides of the outer peripheral part of the common member; theannular bracket sections are fitted to the outer surfaces of therespective shoulder sections of the first casing and the second casing;and the stator is located around and outside the common member.
 7. Themotor-mounted internal gear pump according to claim 2, wherein the pumpcasing is made of PPS carbon fiber resin as PPS resin containing carbonfiber or PPS glass fiber resin as PPS resin containing glass fiber. 8.The motor-mounted internal gear pump according to claim 2, wherein theinner rotor is made of PPS carbon fiber resin as PPS resin containingcarbon fiber, or POM resin.
 9. The motor-mounted internal gear pumpaccording to claim 6, wherein the first casing and the second casing aremade of PPS carbon fiber resin as PPS resin containing carbon fiber. 10.The motor-mounted internal gear pump according to claim 9, wherein: anouter peripheral part of either of the first casing and the secondcasing is extended axially to form a can for sealing between the rotatorand the stator; and the stator is fitted outside the can.
 11. Amotor-mounted internal gear pump, comprising: a pump part which sucksand discharges hydraulic fluid; and a motor part which drives the pumppart, the pump part including: an inner rotor with teeth on its outersurface; an outer rotor with teeth on its inner surface to mesh with theteeth of the inner rotor; and a pump casing which houses the inner rotorand the outer rotor; and the motor part including: a rotator; and astator which rotates the rotator, wherein the rotator is made of PPSresin/ferrite bond magnet as PPS resin containing ferrite magneticpowder.
 12. The motor-mounted internal gear pump according to claim 11,wherein: the pump casing is made of PPS carbon fiber resin as PPS resincontaining carbon fiber; and the inner rotor is made of PPS carbon fiberresin as PPS resin containing carbon fiber.
 13. Electronic equipment,wherein the motor-mounted internal gear pump according to claim 1 ismounted as a liquid circulation source and an antifreeze liquid composedof water and an organic substance is used as the hydraulic fluid.